If you wanted to run a 800 foot long 200I, 240E, single phase underground feeder(pole mounted meter to a house 800 feet away) it looks like you would need 750kcmil Alum to get your VD around 3% for the feeder. What could be some of the pitfalls of doing this? Besides have a ton of money in the ground that is the customers responsiblity? The calcs work out, but I am a little short on the theroy. To bring primary power into the farm would be more expesive then laying in direct burial wire! Any thoughts or comments would be great!
extreme voltage drop
- Thread starter yanert
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charlie
Senior Member
- Location
- Indianapolis
Re: extreme voltage drop
If it is that far, you really need a transformer. Why won't the serving electric utility set one for this installation? What does "200I, 240E" mean, is it 200 amperes at 240 volts? If that is the case, what is the actual load? The voltage drop may not be as severe if you are using calculated load as opposed to the feeder size.
If it is that far, you really need a transformer. Why won't the serving electric utility set one for this installation? What does "200I, 240E" mean, is it 200 amperes at 240 volts? If that is the case, what is the actual load? The voltage drop may not be as severe if you are using calculated load as opposed to the feeder size.
jtester
Senior Member
- Location
- Las Cruces N.M.
Re: extreme voltage drop
I come up closer to 6% drop, from NEC Table 9
750KCMIL Al = .045 ohms/1000'
200 amps X (.045/1000)X 800'X 2 = 14.4 volts
14.4/240 = 6%
Charlie is correct on both counts. Most of the time a 200 amps service doesn't serve a 200 amp load. Your actual load is likely less. Secondly, once you determine your real load you need a step up transformer, and run the circuit at 480 volts, then step it back down to 240 at the the farm.
I come up closer to 6% drop, from NEC Table 9
750KCMIL Al = .045 ohms/1000'
200 amps X (.045/1000)X 800'X 2 = 14.4 volts
14.4/240 = 6%
Charlie is correct on both counts. Most of the time a 200 amps service doesn't serve a 200 amp load. Your actual load is likely less. Secondly, once you determine your real load you need a step up transformer, and run the circuit at 480 volts, then step it back down to 240 at the the farm.
resistance
Senior Member
- Location
- WA
Re: extreme voltage drop
I agree with the above. I was also puzzled by the letters, but it dawned on me that yanert may have been using Ohm letters.
I agree with the above. I was also puzzled by the letters, but it dawned on me that yanert may have been using Ohm letters.
Re: extreme voltage drop
I am still confused? Why the step up the voltage? If you can combat the VD with larger wire why would you still need to step it up and down and take the price hit on the transformers? Like I said I am a little short on the theroy. Just looking for the concrete answer so I can take an abstract electrical theroy problem and put it into a practical application.
I am still confused? Why the step up the voltage? If you can combat the VD with larger wire why would you still need to step it up and down and take the price hit on the transformers? Like I said I am a little short on the theroy. Just looking for the concrete answer so I can take an abstract electrical theroy problem and put it into a practical application.
Re: extreme voltage drop
My caculations give a voltage drop for 750kcm AL
of 14 volts and 6% VD for 200 amps. You are asking for trouble with this installation. VD for 100 amps actual load is 3%. Assuming the actual load is 100 amps and your A/C starts the the voltage drops to 7.2%. Flicker problem. Customer complains. What happens when the customer wants to add load?
If you use a step up transformer 480 volts and 100 amps you can use #1 Cu and get a VD of 5.2%.
You use the taps to correct the 5.2% and you are back to zero. It does take 2 transformers though.
Which is cheaper, transformers and #1 cu or 800 ft of 750 AL?
My caculations give a voltage drop for 750kcm AL
of 14 volts and 6% VD for 200 amps. You are asking for trouble with this installation. VD for 100 amps actual load is 3%. Assuming the actual load is 100 amps and your A/C starts the the voltage drops to 7.2%. Flicker problem. Customer complains. What happens when the customer wants to add load?
If you use a step up transformer 480 volts and 100 amps you can use #1 Cu and get a VD of 5.2%.
You use the taps to correct the 5.2% and you are back to zero. It does take 2 transformers though.
.
Which is cheaper, transformers and #1 cu or 800 ft of 750 AL?
jtester
Senior Member
- Location
- Las Cruces N.M.
Re: extreme voltage drop
yanert
If you step up the voltage from 240 to 480 you get two benefits. 1.) You cut the current in half, which lets you use smaller wire, and 2.) you divide by 480 instead of 240 when figuring percent. That again cuts your percent drop in half. Going from 240 to 480 volts cuts your percent voltage drop by 3/4 or allows you to go down in wire size significantly.
Not obvious at first, but double bang for your bucks.
yanert
If you step up the voltage from 240 to 480 you get two benefits. 1.) You cut the current in half, which lets you use smaller wire, and 2.) you divide by 480 instead of 240 when figuring percent. That again cuts your percent drop in half. Going from 240 to 480 volts cuts your percent voltage drop by 3/4 or allows you to go down in wire size significantly.
Not obvious at first, but double bang for your bucks.
Re: extreme voltage drop
Yanert -
I think 750kcmil AL is about $6 per foot. For 2400 feet, that is $15,000. 4/0Al is $2 per foot and you only need 1600 feet. (2W 480V or 600V ungrounded direct burial) that is about $3200. That leaves you lots of money to spend on the transformers
I checked a SQD catalog and 25kVa 240/480V tramsformers are $2200 each and you can probably get them for 60% of that. You will also need a 600V, 2pole, 100 A fused disconnect for the second transformer primary.
I would not skimp on the conductors for the 480V 2W link. The transformers also have some impedance, that will add to the Vd and the regulation. So keep the wire fat.
I would worry more about the regulation than the Vd. You can fix the Vd with the transformer taps, But the regulation will still suffer and poor regulation blinks the lights just as bad as high Vd.
This is an economic issue. Get some prices and the answer should be clear.
carl
Yanert -
I think 750kcmil AL is about $6 per foot. For 2400 feet, that is $15,000. 4/0Al is $2 per foot and you only need 1600 feet. (2W 480V or 600V ungrounded direct burial) that is about $3200. That leaves you lots of money to spend on the transformers
I checked a SQD catalog and 25kVa 240/480V tramsformers are $2200 each and you can probably get them for 60% of that. You will also need a 600V, 2pole, 100 A fused disconnect for the second transformer primary.
I would not skimp on the conductors for the 480V 2W link. The transformers also have some impedance, that will add to the Vd and the regulation. So keep the wire fat.
I would worry more about the regulation than the Vd. You can fix the Vd with the transformer taps, But the regulation will still suffer and poor regulation blinks the lights just as bad as high Vd.
This is an economic issue. Get some prices and the answer should be clear.
carl
poweringtech
Member
Re: extreme voltage drop
Yanert
Maybe a buck boost transformer will do instead of a regular induction type transformer. You can check specs in SQD catalog
Yanert
Maybe a buck boost transformer will do instead of a regular induction type transformer. You can check specs in SQD catalog
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: extreme voltage drop
A boost transformer cannot be used on a varying load as it will create an over voltages when the load drops off. The voltage drop is created in the supplying wire and will still be there after the boost transformer. Just at a higher voltage. This could be very damaging to equipment.By
Yanert
Maybe a buck boost transformer will do instead of a regular induction type transformer. You can check specs in SQD catalog
BAHTAH
Senior Member
- Location
- United States
Re: extreme voltage drop
In my area we have many large ranches where the utility provides power to the property line and the owners don't want to grant any easements for utility lines to their buildings. Typically where the distances are great as in your case and their is a possibility of power requirements at other buildings in the future we will install a free-standing service switchboard at the property line and back-feed small oil-filled clam shell transformers (like those used by utilities) stepping the voltage up to 5kv. By doing this we have a secure transformer that is not effected by the weather (rain, dust, kids etc) and we need only run a single conductor with fully rated neutral wire shield to another transformer to be stepped down for the residence. In addition we install lightning arrestors on the primay (5kv)k positions. These transformers are very cost effective and voltage drop becomes a non issue. If another building requires power in the future you can plug a load-break elbow into the transformer at the dwelling and extend the 5kv to another transformer.
In my area we have many large ranches where the utility provides power to the property line and the owners don't want to grant any easements for utility lines to their buildings. Typically where the distances are great as in your case and their is a possibility of power requirements at other buildings in the future we will install a free-standing service switchboard at the property line and back-feed small oil-filled clam shell transformers (like those used by utilities) stepping the voltage up to 5kv. By doing this we have a secure transformer that is not effected by the weather (rain, dust, kids etc) and we need only run a single conductor with fully rated neutral wire shield to another transformer to be stepped down for the residence. In addition we install lightning arrestors on the primay (5kv)k positions. These transformers are very cost effective and voltage drop becomes a non issue. If another building requires power in the future you can plug a load-break elbow into the transformer at the dwelling and extend the 5kv to another transformer.
charlie
Senior Member
- Location
- Indianapolis
Re: extreme voltage drop
Grant, I am not familiar with the term "clam shell" type transformers. Are you referring to a standard pad mounted, dead front type transformer where the front of the enclosure opens like a "clam shell"?
Also, in light of 410.75 (I know it doesn't apply here), how do you justify making that voltage available to the homeowner who knows nothing about medium voltage?
Grant, I am not familiar with the term "clam shell" type transformers. Are you referring to a standard pad mounted, dead front type transformer where the front of the enclosure opens like a "clam shell"?
Also, in light of 410.75 (I know it doesn't apply here), how do you justify making that voltage available to the homeowner who knows nothing about medium voltage?
Re: extreme voltage drop
Charlie
He must be speaking of pad mount transformer because he extends the primary by using a load break elbow on the transformer. I don't see a problem with this installation If the cable fails the customer is out of service until he calls an EC who has the knowledge to fix it.
I don't see where 410.75 fits in.
Grant
Do you direct bury the cable or use PVC? What utility serves this area?
AS far as the original post I don't see why the utility won't install 2 poles and a transformer to provide power to the house. Thats what they are in business for.
Charlie
He must be speaking of pad mount transformer because he extends the primary by using a load break elbow on the transformer. I don't see a problem with this installation If the cable fails the customer is out of service until he calls an EC who has the knowledge to fix it.
I don't see where 410.75 fits in.
Grant
Do you direct bury the cable or use PVC? What utility serves this area?
AS far as the original post I don't see why the utility won't install 2 poles and a transformer to provide power to the house. Thats what they are in business for.
BAHTAH
Senior Member
- Location
- United States
Re: extreme voltage drop
Charlie, The transformers in question are typically the ANSI Type1 or Type-2 with the flip top hood. They are oil-filled dead front with primary bushing wells that allow for series connection of the primary single-phase from one transformer to the next or in the case of a utility they will have an actual loop system on the primary so the primary supply can be in either direction. The transformers also have bayonet fusing on the primary.What I like about using the higher voltage is obvious with respect to voltage-drop, however the transformers have pad locking ability as well as a pentahead bolt that must be in place prior to locking and cannot be removed unless the lock is removed. Unlike a standard vented transformer with rain shield (N3R) I don't have to worry about some kid shoving a stick into it because he/she sees it sitting out in some field away from anything or snow, dust etc. The primary cable is installed in PVC conduit underground and all the terminations are done using load-break elbows. The system has lightning arrestors for added protection and at each building the secondary is treated as a typical service. In my view it is a much more secure installation with respect to customer access. The transformers are locked by the contractor and even if someone cuts the lock they still need the special socket to remove the bolt. unlike a standard vented transformer where the customer can just remove the cover and be looking 480V. I understand your concern of a higher voltage for a residence however the buildings never see the primary which is actually more secure than if I used 480V. I do not know of any voltage limitation for a customer distribution systems on large properties and have not had our inspecting authority question the installations.
Charlie, The transformers in question are typically the ANSI Type1 or Type-2 with the flip top hood. They are oil-filled dead front with primary bushing wells that allow for series connection of the primary single-phase from one transformer to the next or in the case of a utility they will have an actual loop system on the primary so the primary supply can be in either direction. The transformers also have bayonet fusing on the primary.What I like about using the higher voltage is obvious with respect to voltage-drop, however the transformers have pad locking ability as well as a pentahead bolt that must be in place prior to locking and cannot be removed unless the lock is removed. Unlike a standard vented transformer with rain shield (N3R) I don't have to worry about some kid shoving a stick into it because he/she sees it sitting out in some field away from anything or snow, dust etc. The primary cable is installed in PVC conduit underground and all the terminations are done using load-break elbows. The system has lightning arrestors for added protection and at each building the secondary is treated as a typical service. In my view it is a much more secure installation with respect to customer access. The transformers are locked by the contractor and even if someone cuts the lock they still need the special socket to remove the bolt. unlike a standard vented transformer where the customer can just remove the cover and be looking 480V. I understand your concern of a higher voltage for a residence however the buildings never see the primary which is actually more secure than if I used 480V. I do not know of any voltage limitation for a customer distribution systems on large properties and have not had our inspecting authority question the installations.
BAHTAH
Senior Member
- Location
- United States
Re: extreme voltage drop
Bob, You are correct, these are pad-mount single-phase oil-filled transformers. The utility in this area is Sierra Pacific Power Company, Plumas Rural Electric Coop and various other rural utilities depending where you are in the state. These installations work well from a cost stand point when a utility wants 20-30K to install power to a single dwelling on a large ranch. I have had some customers that just refuse to deal with the utility. Like most things it comes to cost.
Bob, You are correct, these are pad-mount single-phase oil-filled transformers. The utility in this area is Sierra Pacific Power Company, Plumas Rural Electric Coop and various other rural utilities depending where you are in the state. These installations work well from a cost stand point when a utility wants 20-30K to install power to a single dwelling on a large ranch. I have had some customers that just refuse to deal with the utility. Like most things it comes to cost.
charlie
Senior Member
- Location
- Indianapolis
Re: extreme voltage drop
"I don't see where 410.75 fits in."
Bob, it doesn't except for the prevention of Joe Homeowner from contacting the higher voltage. Grant has taken care of that to some extent.
Grant, we use that type of transformer on a fiberglass box pad for training the cable. The question I have is if the customer owns the transformers, how do you keep him from have the key to the locks and sockets for the pentahead bolts.
"I don't see where 410.75 fits in."
Bob, it doesn't except for the prevention of Joe Homeowner from contacting the higher voltage. Grant has taken care of that to some extent.
Grant, we use that type of transformer on a fiberglass box pad for training the cable. The question I have is if the customer owns the transformers, how do you keep him from have the key to the locks and sockets for the pentahead bolts.
Re: extreme voltage drop
And, I would add, why would anyone want to? It is their's, paid for by them, on their property. And certainly no more dangerous than the combine, the 400hp truck, the rifles, the rat poison ....
My inclination would be anybody smart enough to take care of themselves on a remote ranch, not stick their arms in a snake pit or a bear's mouth, likely is smart enough to not stick their hands in an HV box.
Just a thought -
And, I would add, why would anyone want to? It is their's, paid for by them, on their property. And certainly no more dangerous than the combine, the 400hp truck, the rifles, the rat poison ....
My inclination would be anybody smart enough to take care of themselves on a remote ranch, not stick their arms in a snake pit or a bear's mouth, likely is smart enough to not stick their hands in an HV box.
Just a thought -
charlie
Senior Member
- Location
- Indianapolis
Re: extreme voltage drop
WOW, that is a convincing argument! I yield.
WOW, that is a convincing argument! I yield.
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: extreme voltage drop
Now I know why there are so many out there that have no common sense.
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